While not true marine mammals, river otters do use and rely on marine resources. The expansion of their populations since the early 1900s is a true conservation success story. Ecosystem recovery efforts and river otter reintroductions restored otter populations to much of their historic range. River otters often live in small social groups that include mother and offspring or other unrelated adults.
North American river otters (Lontra canadensis) inhabit inland freshwater environments; however, from Alaska to California they also occur in coastal marine waters where they forage on a variety of marine fish and invertebrates. Little is known about mortality factors in marine-foraging river otters. Among 30 otter carcasses collected in San Juan County, Washington, analysis indicates that car collisions and gunshots were the most common causes of mortality.
North American Otter - Northern River Otter - River Otter - loutre de rivière
Informal Taxonomy
Animals, Vertebrates - Mammals - Carnivores
Formal Taxonomy
Animalia - Craniata - Mammalia - Carnivora - Mustelidae - Lontra - Patterns of genetic variation do not concur with current subspecific designations (Serfass et al. (1998), and numerous translocations have crossed subspecies' range boundaries; hence the use of subspecific names is not meaningful in many cases.
Ecology and Life History
Short General Description
A large mustelid (otter).
Habitat Type Description
Freshwater
Migration
true - false - false
Non-migrant
true
Locally Migrant
false
Food Comments
Feeds opportunistically on aquatic animals, particularly fishes (mostly slow-moving, mid-size species), frogs, crayfish, turtles, insects, etc., sometimes birds and small mammals. In coastal waters eats marine species (Bowyer et al. 1995). Commonly preys on nesting seabirds in some areas (e.g., Alaska islands). See Toweill and Tabor 1982 for many further details.
Reproduction Comments
Implantation is delayed 8 months or more. Gestation, including delayed implantation, lasts 9-12 months. In many areas, births peak in late winter-early spring; parturition dates may not be closely synchronized within a given population. Litter size is 1-6 (average 2-3); 1 litter per year. Young may first enter water at about 7 weeks, are weaned at about 3 months, stay with mother for about a year. Male may rejoin family after young leave den. Females breed for the first time at 2 years. Males become sexually mature at 2 years, but may not breed successfully until 5-7 years old. Females evidently breed in alternate years in some areas (e.g., Alabama, Georgia), every year in Oregon (see Toweill and Tabor 1982).
Ecology Comments
Home range typically is linear; 20-30 miles for a pair or male; less for females with young (Jackson 1961). May hunt over as much as 80-100 km of stream during the course of one year. In coastal Alaska, summer home range size averaged around 20 km of shoreline in males, 10 km in females, with ranges twice as large in oiled areas (Bowyer et al. 1995). <br><br>Population density of one per 2.2 miles has been recorded (Baker 1983). Density was estimated at one otter per 86 ha of coastal marsh in Louisiana (Shirley et al. 1988). In Idaho, density was one family group and 1-3 subadults or nonbreeding adults per 15 km of waterway, plus one breeding adult male for each 20-30 km of waterway (see Toweill and Tabor 1982). Density in coastal areas of the Gulf of Alaska was 0.30-0.85 otters/km of shoreline (Testa et al. 1994, Bowyer et al. 1995).
Length
131
Weight
13600
Conservation Status
NatureServe Global Status Rank
G5
Global Status Last Reviewed
1996-11-18
Global Status Last Changed
1996-11-18
Distribution
Conservation Status Map
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Global Range
FG - 20,000-2,500,000 square km (about 8000-1,000,000 square miles) - FG - Throughout most of North America north of Mexico, except the extreme southwestern U.S. Extirpated from large areas of the interior U.S. following European colonization. Has been reintroduced in some parts of the range (e.g., Colorado, Virginia).
Global Range Code
FG
Global Range Description
20,000-2,500,000 square km (about 8000-1,000,000 square miles)